They were taken to a nearby hospital with non-life threatening injuries.
Police say no arrests were immediately made, but a knife was recovered on the sidewalk.
The club, which opened in 1979, helped define the East Village scene in its early years by hosting acts like Madonna and Blondie.
Bands like Nirvana and the Red Hot Chili Peppers are believed to have played their first city concerts there.
It is housed in a four-story tenement building that a local preservation organization is pushing to be landmarked.